Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium, glass, fabric, metal, or other objects as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a visible image. Note that the visible image may not be visible to the naked eye depending on the composition of the toner particles (e.g., clear toner).
After the latent image is developed into a visible image on the photoreceptor, a suitable receiver is brought into juxtaposition with the visible image. A suitable electric field is applied to transfer the toner particles of the visible image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (“fuse”) the print image to the receiver. Plural print images, e.g., of separations of different colors, are overlaid on one receiver before fusing to form a multi-color print image on the receiver.
Electrophotographic (EP) printers typically transport the receiver past the photoreceptor to form the print image. The direction of travel of the receiver is referred to as the slow-scan, process, or in-track direction. This is typically the vertical (Y) direction of a portrait-oriented receiver. The direction perpendicular to the slow-scan direction is referred to as the fast-scan, cross-process, or cross-track direction, and is typically the horizontal (X) direction of a portrait-oriented receiver. “Scan” does not imply that any components are moving or scanning across the receiver; the terminology is conventional in the art.
In most electrophotographic development systems, more toner is supplied to the photoreceptor than is necessary to develop the visible image. This provides improved reproduction of large areas of high density on the print. Some of the excess toner can leave the confines of the development station. This toner can contaminate other areas of the imaging module, reducing image quality and printer reliability. Toner can leave the development station through the leading edge, where the charged, un-toned photoreceptor enters the station, or through the trailing edge, where the visible image on the photoreceptor is exiting the development station. Various attempts have been made to reduce contamination. “Contamination” and “dusting” are used synonymously herein, and both refer to airborne particles, e.g., toner particles, being deposited on components of the printer on which they are not intended to be deposited. Dusting in a two-component developer can also occur when toner particles are not sufficiently tribocharged before being agitated. Since the toner particles are not electrostatically attracted to the carrier particles, the toner particles can become airborne more easily than they would if they carried more charge.
For example, seals have been employed on the development station. These can include flaps, plushes, or brushes that make direct contact with the surface of the photoconductor. Seals are generally located on the leading edge of the development station, before development occurs, since the nap created by the developer can seal the trailing edge. Elastomeric seals can be formed from, e.g., polyethylene terephthalate (PET), polyurethane (PUR), polyphenylether (PPE), polycarbonate (PC), polyethylene (PE), polyolefin, and polypropylene (PP). Seals can also be formed from foams, fabrics, rigid plastics, or metals. However, more rigid seal materials increase the risk of damage to the roller in contact with the seal.
U.S. Pat. No. 5,467,174 to Koga, column 6, describes a sealing member provided at the opening of a development unit and in light contact therewith. However, a light seal can be bypassed by sufficiently small particles. Moreover, a light seal only restricts the travel of particles in one direction.
Commonly-assigned U.S. Pat. No. 5,991,568 to Ziegelmuller et al., the disclosure of which is incorporated herein by reference, describes reducing the amount of toner escaping from a cleaning housing. Ziegelmuller describes a dust seal blade that creates a cavity in front of the cleaning blade to capture airborne toner dust, thereby reducing contamination of a cleaning blade engaged with the surface to be cleaned. Ziegelmuller also describes foam and brush seals and upstream sealing blades.
U.S. Publication No. 2010/0028045 to Kawakami et al. describes a cleaning device for a rotary member. The cleaning device includes a seal and a blade pressed against the rotary member and seal extending along the length of the rotary member. The gaps between the seal and the blade at each end of the rotary member are sealed by pressing respective end seals against the rotary member. However, the mechanical contact between the end seal and the rotary member can wear or damage the rotary member. Kawakami suggests that a very limited range of materials (foams, fabrics) can be used to reduce these risks; these limits reduce opportunities to combine part functions and can therefore lead to increased size, weight, and cost of a printer.
Although these devices provide a seal and reduce the loss of toner dust from the development station, mechanical-contact seals can collect material between the seal and the photoconductor, which can in turn scratch the surface of the photoconductor, reducing image quality. Various alternative seal techniques have been tried.
GB 2 098 095 A to Kopp et al. describes a toner dust sealing plate extending close to the photoconductor at the trailing edge of the development station and a vacuum system to reduce dusting out of the leading edge of the development station. Vacuum systems can be noisy and expensive. Moreover, vacuum systems need to be carefully tuned to avoid sucking toner out of the development station.
GB 2 098 096 A to Maier et al. describes a guide means that divides the development station into upper and lower parts. Toner flows from the upper to the lower part around both ends of the guide means, so dust generated in the lower part cannot escape to the upper part. This scheme requires a more complicated development station and can limit the functions that can be performed by or in the development station.
Commonly-assigned U.S. Pat. No. 6,385,236 to Hilbert et al., the disclosure of which is incorporated herein by reference, describes compliant lip seals around roller axles and permanent magnets used as magnetic seals to prevent leakage of developer material from the ends of the development roller. Although useful, this requires magnets; less-expensive seal materials are desirable. Magnetic seals form a “brush” with the magnetic material (e.g. developer) that contacts the moving member and can cause wear or damage to the member.
There is a continuing need, therefore, for an improved seal that reduces dusting in an electrophotographic printer without damaging the photoreceptor.